Thermionic valve of the screened grid type



Jan. -112, 1937. I w. R. BULLIMORE THERMIONIC VALVE OF THE SCREENED GRID TYPE Filed Sept. 9, 19:51 2 Shets-Sheeft 1 INVERTOR William R..Bu 111mor"e A fi I I.

ATTORNE! Jan. 12, 1937. v w. R. BULLIMORE THERMIONIC VALVE OF THE SCREENED GRID TYPE Filed'Sept. 9, 1931 2 Sheets-Sheet 2 INVENTOR William R. Bullimore ATTORQY Patented Jan. 12, 1937 THERMIONIC VALVE OF THE SGREIENED GRID TYPE William Richard Bullimore, London, England Application September 9, 1931, Serial No. 561,928 In Great Britain December 11, 1930 11 Claims. ((31. 250-275) This invention relates to thermionic valves for use in radio receiving apparatus and other purposes and has particular reference to valves of the type in which an electrostatic screen is disposed between an anode and a control electrode for the purpose of screening the control electrode from elfects due to electrostatic coupling between the anode and the control electrode.

The objects of the present invention are to provide an improved method of constructing and mounting the electrostatic screen, an improved method of mounting the various electrodes in interspaced relationship to ensure rigidity of construction in all conditions and absence of short circuits between any two electrodes, and a simplified method of manufacturing electrode assemblies which lends itself readily to mass production methods.

According to the present invention, an electrostatic screen or screening grid for a thermionic valve and of the kind constructed as a closed box or cage in which the control electrode to be screened is substantially entirely enclosed, is provided, wherein such box or cage comprises parallel sides formed of wire windings connected at their vertical edges by imperforate sheet metal elements.

According to the preferred form of the invention the screening element is built up on a sheet metal base plate by securing the sheet metal portions of the screening element to members projecting upwardly from the base plate which is rigidly mounted relatively to the re-entrant tube of the valve. The screening element may also be utilized according to a further feature of the invention as a support for another electrode or electrodes by mounting thereon insulating elements which serve for supporting and positioning other electrodes, conductors or supports.

Reference will now be made to the accompanying drawings which illustrate by Way of example constructions according to the invention and in which:

Figure 1 is a sectional elevation of an electrode assembly including a wire filament,

Figure 2 is a sectional plan of Figure 1,

Figure 3 is an elevation of the electrostatic screen,

Figure 4 is a perspective view of the anode and its supports,

Figure 5 is a fragmentary elevation showing the connections of the anode conductors,

Figure 6 is a sectional elevation of an electrode assembly including an indirectly heated cathode,

Figure 7 is a sectional elevation showing the application of the'invention to a valve of the pentode type,

Figure 8 is an external elevation partly in section of the arrangement shown in Figure 7,

Figure 9 is an enlarged detail view showing the construction of a wire screen which forms part of the screen electrode and Figure 10 is a diagrammatic view similar to Figure 9 showing a modified form of screen.

Referring first to Figs. 1, 2, and 3 the screening element is built up on a sheet metal base plate 1 by welding channel shaped sheet metal side pieces 2 to lugs 3 extending upwardly from the base plate I. This plate is secured to the reentrant tube or press d of the valve by means of conductor supports 5 and is preferably formed with a depending flange or skirt 6 to screen the anode (hereinafter described) from the various leading-in conductors which are mounted in the tube 4. The base plate I! is formed with a central rectangular aperture around which the electros'tatic screen is disposed and through which pass the conductors and supports for the cathode and control electrode.

The wire portion l of the screening element is preferably formed byv winding on notched or serrated posts 9 and in order to ensure uniformity and equispacing between the adjacent wires of the winding and to prevent displacement the posts 9 are notched equidistantly and the wire constituting the screen is wound round the posts in the notches in a helical manner as shown in Fig. 9 so as to form two parallel layers of wires separated from one another by the thickness of the posts 9. Owing to the helical winding the lengths of wire in one layer will be equispaced between the lengths of wire in the other layer. Two or more wires can be wound parallel to one another, an example of such construction being shown in Fig. 10 in which two wires are employed one being shown thicker than the other for the purpose of distinction only, the wires in practice being of the same thickness. Those parts of the wires which lie behind the posts s are shown in broken lines in Fig. 10. After winding, the two wire screens 7 are fixed between the metal channels 2 which totally enclose their edges and these metal channels are subsequently welded or otherwise secured to imperforate metal channels 3 Which form constituent parts of the end walls of the electrostatic screen. By constructing the screens in the manner above described with reference to Figs. 9 and 10 the maximum screening effect is obtained through the screens as each screen is composed of two parallel layers of wire so arranged that the wires of one layer are spaced between those of the other layer.

The base plate I has metal brackets it] formed thereon or attached thereto for the purpose of supporting an insulating plate ii to which the lower edges of the anode elements are connected. The insulating plate is preferably formed of mica shaped so as to fit closely around the exterior of the electrostatic screen and the upper ends of the anode elements l2 are connected to a second and similar insulating plate 53 so as to maintain them in correct equispaced relationship with the screen at all times throughout the life of the valve. The connection, as shown in Fig. 4 is by means of lugs M passed through slots in the plates and bent over at right angles to fix the two elements together. The upper end of the electrostatic screen is closed by a mica plate I5 which is slotted at It to enable a spring support I! for a filament iii to be passed therethrough. The plate I5 is also perforated to position the upper ends, of wires 19, of a control electrode 2%, the lower ends of these wires being carried by supports 2! mounted in the tube 4. Around the wires l9 near their upper ends is mounted a further mica plate 22 above which the spring ll bears and through which passes a wire 23 connected to the bight of the filament l8 so as to maintain it under the requisite tension. The lower ends of the filament are connected to conductors 24.

Above the upper end of the electrostatic screen is disposed a sheet metal cap in the form of a rectangular box 25 which is carried by prolongations 26 of two of the wires 9 on which the sides of the screen are wound. This cap, which is open at its under side, is disposed in such manner as to be held out of contact with the control electrode or the filament. The two parallel plates l2 which constitute the anode are connected by conductors 2'! (see Fig. 5) joined above the cap 25 to a common conductor 28 which connects them to a terminal mounted at the end of the vitreous envelope of the valve remote from the re-entrant tube 4.

In the form of construction illustrated in Fig. 6, the electrostatic screen, its base and cap and the anode are identical with those illustrated in Fig. 1 but in this construction an equipotential cathode is employed instead of a filament, this cathode being in the form of a tube 29 closed at its lower end where it is mounted on a conductor support 30 and open at its upper end for the entry of a heating wire 3i connected to conductor supports 32. In this form of construction only one mica plate 33 is disposed within the electrostatic screen and serves to position not only the cathode 29 but also the members 32 as well as the grid wires 34.

Figures '7 and 8 show the application of the invention to a valve of the pentode type and in this form of the invention two additional wire screens 35 are mounted between the anode plates and the wire portions of the electrostatic screen, which is constructed as shown in Fig. 3.

The wire screens 35 are wound on supporting wires 36 which are mounted in the mica plates II and i3 and one of the wires 36 has a down- Ward extension connected to a wire 31 the other end of which is connected to the lower end of an equipotential cathode 38. As this cathode has no conductor support from the re-entrant tube 4 it is maintained in equispaced relationship with the control electrode by means of mica plates 39 and ill mounted around the upper and lower ends of the wires 3% which carry the control electrode. The screens 35 are inter-connected at their upper ends by a short length of wire ii.

In all the forms of construction above described the electrodes and their supports are prevented by the various mica plates, from becoming displaced during use, thus preventing short circuits from occurring between any two electrodes. The complete rigidity of construction obtained also ensures that valves of the same type have substantially uniform characteristics.

The method of construction described also facilitates manufacture as by making the brackets Id of standard dimensions the anode is automatically positioned in passing it over the electrostatic screen and no gauging is therefore necessary in assembling these electrodes. The internal mica plate or plates also serve for positioning the supporting wires for the control electrode and filament during assembly.

I claim:

1. A thermionic valve comprising a cathode, a control electrode and an electrostatic screen having parallel sides at opposite sides of the control electrode formed respectively of wire windings each providing twoparallel layers of wires, and imperforate sheet metal elements embracing and connecting the vertical edges of said windings to form a closed structure in which the control electrode is substantially entirely enclosed and screened.

2. A thermionic valve having an electrostatic screen in the form of a closed box substantially entirely enclosing a control electrode and comprising sides at opposite sides of the control electrode and composed respectively of wire windings, each providing two parallel layers of wires, ends of imperforate sheet metal channels embracing and connecting the edges of said windings, a metallic base to which ends of said channels are rigidly and directly connected for supporting the assembly and a metallic cap closing the top thereof.

3. A thermionic valve according to claim 1 wherein spaced insulating plates fitting closely around the exterior of the screen serve as supports for at least one electrode thereby maintained in correct interspaced relationship with said screen.

4.. A thermionic valve according to claim 1 wherein a pair of spaced insulating plates are fitted closely around the exterior of said screen and carry two metal plates constituting an anode, each of said metal plates extending between and being secured at its ends to said insulating plates.

5. A thermionic valve, according to claim 1 wherein insulating plates mounted around the exterior of said screen carry two metal plates at opposite sides of the screen constituting an anode and two additional wire screens interposed between said metal anode plates and the respective sides of said electrostatic screen.

6. An electrostatic screen for a thermionic valve comprising opposed spaced sides each composed of a winding providing two parallel layers of wires, ends formed of imperforate separate reversely arranged sheet metal channels in which the vertical edges of said windings are fixed, said channels closing the space between said windings at the vertical edges thereof, a rectilineal sheet metal cap and a metallic base plate, the Whole substantially entirely enclosing a control electrode.

'7. A thermionic valve including an electrostatic screen of box-like form having its endsclosed by parallel imperiorate metal elements and its sides composed respectively of wire windings each providing two parallel layers of wires, insulating plates fitting closely around the exterior of said screen, anode elements carried by said plates, an insulating plate carried internally of said screen for supporting and interspacing electrodes and their supports and a metallic cap on said screen.

8. A thermionic valve including an electrostatic screen of box-like form having its ends closed. by parallel imperforate metal elements and its sides composed respectively of wire windings each providing two parallel layers of Wires, insulating plates fitting closely around the exterior of said screen, anode elements carried by said plates, an insulating plate mounted within said screen for supporting a cathode, a second insulating plate within said screen for positioning a control electrode and metal cap on said screen.

9. A thermionic valve including a base plate supported from the foot of the valve, an electrode rigidly fixed to said base plate, and a plurality of insulating plates extending around said electrode, and at least one insulating plate extending transversely within said electrode to maintain other electrodes, conductors and supports rigidly in their correct spaced positions, and brackets fixed to the base plate and embracing one of said insulating plates for supporting it.

10. A thermionic valve including a base plate supported from the foot of the valve, an electrostatic screen fixed to said base plate, insulating plates mounted upon and extending around the [exterior of said screen, an anode carried by I said plates, brackets fixed to and projecting upwardly from the base plate and embracing the peripheral edge of one of said insulating plates for supporting it and the anode, and at least one insulating plate mounted within said screen to support and position a cathode and control electrode.

11. An electrode assembly for a thermionic valve comprising an electrode having parallel imperforate metal channel members fixed to its opposite edges and rigidly supported from the foot of the valve, two insulating plates extending around the exterior of said electrode for the support of a second electrode, a third insulating plate extending between said channel members for maintaining a third electrode in correct spaced relationship with the other two, and an insulating plate carried by said third electrode for positioning a cathode.

WILLIAM RICHARD BULLIMORE. 

